It is known to use tubular consolidation elements in the consolidation of soils and the like, for example, of an excavation wall or of a mass of soil which may be, for example, a tunnel face or roof or a mine gallery or any underground or exposed mass of soil. Non-return valves are provided in tubular consolidation elements of this type for the injection of consolidating liquids such as cementitious or chemical mixtures.
So-called “consolidation injections” represent one of the best solutions in soil consolidation. This technique involves the formation of a series of drill holes in the ground or soil undergoing consolidation, into which corresponding elongate tubular elements are inserted. Each of these tubular elements, which may also have reinforcing functions, is hollow and has one or more holes in its lateral surface. A consolidation material in the fluid state, generally liquid cement or a functionally similar mixture, is injected into the tubular element, emerges from the holes in the lateral surface of the tubular element, and permeates and penetrates the soil region surrounding the drill hole. The setting of the injected material stiffens the soil, consolidating it.
The tubular element has, in general, several radial holes arranged various distances apart along the tubular element. Normally, instead of a single hole at a certain position along the length of the tubular element, it is preferred to provide a group of two or more holes and, in this case, the radial holes of each group are arranged on the same circumference, spaced apart angularly to a predetermined extent. A special external valve, also known as a “manchette valve” is fitted in the vicinity of each individual hole or group of two or more holes and acts as a non-return valve with respect to the consolidation material that is injected into the tubular element. In fact, the valve opens as a result of the pressure of the injection of the consolidation material into the tubular element, allowing the material to emerge from the radial holes into the surrounding soil region. The valve then closes almost hermetically when the pressure ceases so as to prevent an undesired flow of the injected material back into the tubular element.
According to the prior art, the manchette valve is formed substantially by a rubber ring which is fitted on the outside of the tubular element in the vicinity of the individual holes so as to cover them. This resilient rubber ring generally has a width of between about 40 and 60 mm and is fitted manually along the tubular element in the vicinity of one of the groups of radial holes defined in the tubular element. The number of valves thus depends on the number of individual holes or, more preferably, groups of holes defined in the tubular element, which in turn is variable according to need and application.
Clearly, the manchette valves must be efficient and inexpensive in order for the consolidation injection technique to be competitive. It is therefore fundamental that the rubber rings which constitute them should always stay in the correct position, above all during the insertion of the tube in the drill hole.
For this purpose, the prior art provides for the rubber ring which forms the manchette valve to be housed in an annular groove which is at least as wide as the ring and about 2.0-2.5 mm deep and which is produced by the removal of material from the lateral surface of the tubular element in the region of each group of radial holes.
This solution of the prior art has various disadvantages, however; in the first place, there is a decline in the mechanical performance of the tube the lateral surface of which is weakened in the region of each groove or seat for the rubber ring; in the second place, the preliminary machining operations to be performed on the tubular profile are notable and expensive in terms of time since it is necessary to provide for the drilling and for the removal of material in the region of each group of holes.
Another disadvantage is the need to provide two rigid annular elements on the exterior of the tube above and below the rubber ring; these annular elements are glued to the tube radially and prevent movement of the ring in the longitudinal direction, preventing the holes formed radially in the walls of the tubular element being exposed during the introduction of the tubular element into the drill hole in the soil, with the risk of obstruction of the radial holes and the interior of the tubular element, prejudicing the use of the tubular element and the functional capacity of the valves downstream. This means that the axial fitting of each rubber ring must be precise, above all in view of the fact that a tubular element of the type mentioned above may be as much as ten meters or more long.
Other disadvantages of known tubular injection elements are that conventional manchette valves are prone to being detached from their seats, for example, by sliding along the tube or by rolling along it during the movement or the insertion of the tubular elements in the respective drill holes.